1. Field of the Invention
This invention relates to telephone systems. In particular, it relates to an arrangement for enabling a telephone station served by a telephone system to appear busy to incoming calls.
2. Description of the Prior Art
There has been an increasing need in recent years for an arrangement to enable a subscriber to make a telephone station appear busy to incoming calls. For example, a subscriber may wish to make a telephone station appear busy to incoming calls when the subscriber is not at home. Another subscriber having more than one telephone station to serve a business location may elect to make one or more unmanned telephone stations busy to incoming calls during non-rush hours in order that incoming calls may be alternately routed to other manned telephone stations.
In the past, a subscriber made a telephone station busy to incoming calls by removing the telephone station receiver from the switch hook. A problem arises in this method of making a telephone station busy in that the telephone office serving the telephone station recognizes the receiver off-hook signal as a call request and attempts to serve the off-hook telephone station. After a short time interval the telephone office identifies the receiver off-hook signal as a permanent receiver off-hook signal and establishes a connection in response thereto from the telephone station line to a special termination holding line oftentimes referred to as a permanent signal trunk. When a large number of telephone stations are made busy in this manner, the telephone office attempts to establish connections to all off-hook telephone stations. However, the large number of call requests from the off-hook telephone stations, in combination with requests from calling telephone stations, results in a congestion of the telephone office switching equipment and thereby restricts the capacity of the telephone office to complete call connections.
Attempts have been made in the past to solve this problem by equipping each telephone station line with a special line lockout circuit arranged to hold the telephone station line out of service for the duration of the telephone station receiver off-hook condition. Such line lockout circuits relieve the congestion of the telephone office but have disadvantages in that the telephone office must have a line lockout circuit for each telephone station line and each telephone station line so equipped is then held out of service for the duration of the receiver off-hook condition.
Accordingly, a need exists in the art for an arrangement for enabling a subscriber to busy a telephone station to incoming calls without holding the telephone station line out of service. A need also exists for apparatus arranged for selectively establishing connections of calling telephone stations to called telephone stations to respond to a subscriber made-busy one of the called telephone stations by returning busy signals to each calling telephone station.